The processes of birth, change, and death of stars. The term is applied to the changes through the lifetime of a single star, making it quite different from the use of the term in biology, where it is applied to change occurring across generations. The evolution of a star is described by a track showing its temperature and luminosity, which vary over time as the star forms, when its temperature increases rapidly, occupies a position on the main sequence, and leaves it after normal hydrogen burning ceases. The time taken for this process depends on the star’s mass, from billions of years for the Sun down to a few tens of millions for the most massive stars.